Conventionally, for feeding paper currency bills from a cassette storing therein the paper currency bills as paper sheets; a stage, on which the paper currency bills in the cassette are accumulated, is lifted up. By a bundle of the paper currency bills being pressed with appropriate pressure, against a pick roller, which is provided at an upper portion in the cassette and feeds the paper currency bills, the paper currency bills are fed at a constant speed. Such a conveying method has been used. In order to control lifting of a stage in such a technique for feeding and conveying paper currency bills, the lifting is started if pressure detected by a pressure sensor installed at a pickup roller becomes less than a proper range that has been prescribed when one or more paper currency bills have been fed. If the pressure reaches a predetermined value in the proper range, the lifting is stopped. Such feedback control has been used.
Further, in recent years, a technique has been provided, in which plural conveyance speed modes, such as a normal conveyance mode and a high speed conveyance mode, are set beforehand in order to increase conveyance speed of paper currency bills and shorten paper currency bill handling time.
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 05-303674
Patent Literature 2: Japanese Unexamined Patent Application Publication No. 2005-259087
However, when the conveyance speed of paper currency bills is increased, so-called largely damaged paper currency bills, which are paper currency bills that are crumpled and low in stiffness, become susceptible to the increase in the conveyance speed. As a result, the possibility of occurrence of damage to the paper currency bills or a conveyance jam is increased. Therefore, unless the state of the accumulated paper currency bills is known beforehand, the conveyance speed of paper currency bills is difficult to be increased.